Fibers with functional properties have been disclosed for use in textile yarns. Such fibers may be added for the purpose of achieving a particular visual aesthetic, biological function, e.g., antimicrobial activity, thermal buffering effect, e.g., via incorporation of phase-changing materials into the fiber structure, electrical function, e.g., piezoelectric, electrostrictive, electrochromic activity, optical function, e.g., photonic crystal fibers, photoluminesce, luminescence, magnetic function e.g., magnetostrictive activity, thermoresponsive function, e.g., via shape memory polymers or alloys, or sensorial function, e.g., chemical, bio, capacitive, acoustic sensory activity. Such functional composite yarns have been fabricated into fabrics, garments and wearable/apparel articles.
Functional filaments can have inadequate tensile properties for textile manufacture or use. In many cases, a functional textile yarn is not based solely on functional filaments or on a combination yarn where the functional filaments are required to be a stressed member of the yarn. This can be due, for example, to the presence of particulates which have been added to a filament to impart the functionality. In such cases, the particle addition can increase fiber rigidity and/or decrease the breaking strength or decrease the yield strength. Alternatively, functionality may be achieved in such a way that the elastic limit of the functional filament is reduced, such that the fiber can no longer withstand the tensile stresses applied to fibers during conventional textile manufacturing processes.
U.S. Published Pat. Appln No. 2004/0209059 A1, discloses a functional composite yarn containing standard textile fibers and antimicrobial fibers. The standard textile fibers used in this composite functional yarn can, for example, include textile fibers such as nylon, polyester, cotton, wool, and acrylic. Such textile fibers have little or substantially no inherent elasticity. In other words, these standard textile fibers do not impart “stretch and recovery” power to the functional composite yarn. Although the composite yarn of this reference is a functional yarn, textile materials made therefrom would not be expected to provide textile fabrics and constructions therefrom having a stretch potential.
Similarly, WO 03/027365, to Haggard et al., discloses a functional fabric comprising phase-change material containing fibers. This reference discloses functional fibers comprising a sheath made from polyamides, polyesters and mixtures disclosed therein and including other synthetic polymers and a core made from a combination of hydrocarbon waxes, oils, fatty acid esters, and other phase-change materials disclosed therein. While fabrics made from such yarns may have satisfactory phase-changing properties; they would not be expected to possess an inherent elastic stretch and recovery property.
Yarns, fabrics or garments that have both stretch and recovery as well as some other advanced functionality are highly desired. The stretch and recovery property, or “elasticity”, is the ability of a yarn or fabric to elongate in the direction of a biasing force (in the direction of an applied elongating stress) and return substantially to its original length and shape, substantially without permanent deformation, when the applied elongating stress is relaxed. In the textile arts it is common to express the applied stress on a textile specimen (e.g., a yarn or filament) in terms of (a) a force per unit of cross section area of the specimen or (b) force per unit linear density of the unstretched specimen. The resulting strain (elongation) of the specimen is expressed in terms of a fraction or percentage of the original specimen length. A graphical representation of stress versus strain is the stress-strain curve, which is well-known in the textile arts.
The degree to which fiber, yarn or fabric returns to the original specimen length prior to being deformed by an applied stress is called “elastic recovery” In stretch and recovery testing of textile materials, it is also important to note the elastic limit of the test specimen. The “elastic limit” is the stress load above which the specimen shows permanent deformation. The available elongation range of an elastic filament is that range of extension throughout which there is no permanent deformation. The elastic limit of a yarn is reached when the original test specimen length is exceeded after the deformation-inducing stress is removed. Typically, individual filaments and multifilament yarns elongate (strain) in the direction of the applied stress. This elongation is measured at a specified load or stress. In addition, it is useful to note the elongation at break of the filament or yarn specimen. This breaking elongation is that fraction of the original specimen length to which the specimen is strained by an applied stress, which ruptures the last component of the specimen filament or multifilament yarn. Generally, the drafted length is given in terms of a draft ratio equal to the number of times a yarn is stretched from its relaxed unit length.
In view of the foregoing, functional textile yarns with elastic recovery properties that can be processed using traditional textile means to produce knitted or woven fabrics (“functional textile yarns”) continue to be sought. Fabrics and garments substantially constructed from elastic functional yarns can provide stretch and recovery characteristic to the entire construction, thus better conforming to any shape, any shaped body, or requirement for elasticity.